Device and method for controlling the state of an energy accumulator

ABSTRACT

The invention concerns a device and method for checking the state of an accumulator with energy reserve that is connected to a fluid system. According to the invention, the fluid system is first of all pressurized and this fluid is maintained at an operating pressure P F  for at least a time τ so as to ensure the stabilization of this fluid system. Then the pressurisation of the fluid system is stopped and the time Δt taken by the system to pass from a predetermined pressure P 1  to a predetermined pressure P 2 , with P 2 &lt;P 1 &lt;P F , is determined. This period Δt is compared with a predetermined reference time T ref .

The present invention concerns a device and method for controlling thestate of an energy accumulator connected to a fluid system.

Aircraft are generally equipped with several hydraulic circuits, a mainone and at least one auxiliary one, independent and self contained,which permit the actuation of all the aircraft equipment. FIG. 1 depictsschematically such a hydraulic circuit for controlling a flap 1. Thisclosed hydraulic circuit has a fluid reservoir 2 connected by adistribution circuit 3 to a hydraulic actuator 4. Such a distributioncircuit 3 comprises rigid pipes and possibly flexible pipes for themobile connections (brakes, landing gear, etc). The generation ofhydraulic power is provided for example by a variable-output piston pump5.

When the pilot acts on a control 6 such as a joystick, a control signalis sent to a computer 7 that controls a selector 8. In FIG. 1, theselector 8 is in the “retracted” position. One face of this actuator 4receives the hydraulic pressure in an inlet chamber 9 causing a movementof the actuator towards the right. The flap 1 then moves downwards. Theoutlet chamber 10 of this actuator being connected in return to thereservoir 2, the fluid present in this chamber 10 is sent to thereservoir 2. A transmitter 11 sends a status signal for the flap 1 tothe computer 7 for display 12. Naturally, the selector 8 can send thefluid under high pressure to the chamber 9 or to the chamber 10according to the required direction of movement of the flap 1, downwardsor upwards.

It is known that, in order to function effectively, the consumers 4 needa constant nominal pressure in the chambers 9 or 10 according to themanoeuvre to be performed. Rapid manoeuvres then make the nominalpressure drop transiently since the hydraulic pumps are no longer in aposition to ensure the maintenance of this pressure, particularly if theconsumers 4 are situated far from this pressure source. The fluidentering the inlet chamber 9 must in fact be under nominal pressure inorder to make the flap 1 move in an optimum fashion. The fluid at lowpressure being in the outlet chamber 10 returns via a low-pressurehydraulic line BP to the reservoir 2. It is this difference in pressurebetween the inlet 9 and outlet 10 chambers that actuate the flap 1.

An accumulator with an energy reserve 13 is then used, which willrestore its hydraulic energy reserve to the consumer or consumers 4 inorder to maintain the pressure at a level close to the nominal operatingpressure. This accumulator with energy reserve 13 is placed on thehigh-pressure hydraulic line HP between the hydraulic power generator 5and the consumers 4 furthest away from this power generator 5.

This accumulator 13 also makes it possible to absorb the overpressuresgenerated in the hydraulic circuit by the functioning of the consumers4. Damage to structure and equipment of the aircraft during an abruptvariation in pressure in the pipework is thus avoided.

An accumulator with energy reserve 13 comprises two cavities 14, 15(FIG. 2). A first cavity 14 connected to a hydraulic circuit, and asecond cavity 15 in which a gas is trapped under pressure. An elasticwall can be used to delimit these two volumes 14, 15. However, thiselastic wall can lose efficacy through a prolonged contact with thefluid, the pressurised gas in the second cavity 15 then migrating in thefluid for example.

The correct functioning of this accumulator with energy reserve 13 isguaranteed only when the accumulator is correctly pressurised, it isnecessary to regularly check the pressure of the gas present in thesecond cavity 15.

This operation is performed by a maintenance operator by means of apressure gauge 16 for each of the hydraulic circuits of the aircraft.The immobilisation of aircraft on the ground, and the need to employskilled personnel to perform these maintenance operations, gives rise toa significant cost for the airline.

Skilled operators are in fact necessary since, the pressure varying withtemperature, erroneous pressure reading interpretations could arise.

In addition, these accumulators, which are placed inside the apparatus,require the use of supplementary means for transferring the point forreading the pressure of the gas present in the second cavity to amaintenance point situated on the external structure of the aircraft.This pipework, these pressure gauges and all the fixing means have animpact on the weight of the aircraft and therefore on its fuelconsumption, and moreover impair the reliability of the accumulator withenergy reserve and therefore of the hydraulic system on which theaccumulator is mounted.

The objective of the present invention is therefore to propose a deviceand method for checking the pressurisation of an energy accumulatorconnected to a fluid system, simple in their design and in theiroperating method, economical and allowing particularly reliable, preciseand automatic checking of the state of pressurisation of an energyaccumulator.

To this end, the invention concerns a method of checking the state of anaccumulator with energy reserve that is connected to a fluid system.According to the invention, the following successive steps areperformed:

-   -   the fluid system is pressurised,    -   this fluid is maintained at an operating pressure P_(F) for at        least a time τ so as to ensure the stabilisation of the fluid        system,    -   the pressurisation of the fluid system is stopped,    -   the time Δt taken by this system to change from a predetermined        pressure P₁ to a predetermined pressure P₂, with P₂<P₁<P_(F), is        determined,    -   this time Δt is compared with a predetermined reference time        T_(ref).        In various particular embodiments of the method for checking the        state of an accumulator, each having its particular advantages        and capable of many possible technical combinations:    -   the pressure P₂ is the pre-charging pressure of the accumulator,

“Pre-charging pressure” means here the pressure of the gas in the secondcavity of a new accumulator with energy reserve, that is to say thepressure as specified on leaving the factory. This optimum pre-chargingpressure is typically between 180 and 220 bar depending on the gascontained in the second cavity.

-   -   the pressure P₁ is such that 1/10 P_(F)<P₁<P_(F),        Preferably, and for more precision in the measurement, it will        nevertheless be ensured that the interval of time Δt separating        two predetermined pressure measurements P₁ and P₂ is as large as        possible, that is to say the predetermined pressure P₁ is as        close as possible to P_(F).    -   the reference time T_(ref) is determined by steps a) to d) using        a reference accumulator.        The invention also concerns a device specially adapted for        implementing the method described above. This device comprises        an accumulator with energy reserve connected to a high-pressure        line of a fluid system. The fluid system comprises at least one        pump for pressurising the system.

According to the invention, the device comprises:

-   -   a real-time processing unit having a non-volatile memory,    -   at least one pressure detector for measuring the pressure of the        fluid in the high-pressure line, the detector sending to the        processing unit a measurement signal representing the pressure        measured by this detector,    -   and the processing unit comprises electronic means for measuring        the interval of time Δt separating two predetermined pressure        measurements P₁ and P₂, and means for comparing this value Δt        with a reference value stored in the non-volatile memory.

In various embodiments, the present invention also concerns thefollowing characteristics that are to be considered in isolation or inaccordance with all their technically possible combinations:

-   -   the pressure detector is mounted on the high-pressure hydraulic        line of the fluid system where the accumulator with energy        reserve is mounted,    -   the processing unit sends a state signal from the accumulator to        display means.

This state signal informs the operator, the pilot of the aircraft forexample, whether the check test carried out is positive or negative,that is to say whether or not the pressure of the gas in the secondvolume of the accumulator is sufficient. A negative test requires theaccumulator with energy reserve to be changed. These display means canbe connected to an audible alarm.

The device and method for checking the pressurisation of an energyreserve accumulator can advantageously be used for aircraft or boatfluid systems.

The invention will be described in more detail with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic representation of a fluid system controlling themovement of a flap of the prior art;

FIG. 2 is a schematic representation of the means of the prior art forchecking the pre-charging pressure of an accumulator with energy reserveusing a pressure detector with visual display;

FIG. 3 shows schematically a device for checking the state of anaccumulator with energy reserve according to a particular embodiment ofthe invention;

FIG. 4 is a schematic representation of a test of an accumulator withenergy reserve according to a particular embodiment of the method of theinvention.

FIG. 3 shows a device for checking the state of an accumulator withenergy reserve according to a particular embodiment of the invention.

The accumulator with energy reserve is connected to a fluid system. Eachaircraft comprises at least one main fluid system and at least oneback-up fluid system for manoeuvring all the aircraft equipment. Theback-up fluid system provides redundancy for all the vital functions ofthe aircraft. Each fluid system has its own fluid reservoir 17 connectedto a closed fluid distribution circuit 18, which comprises ahigh-pressure line HP and a low-pressure line BP for the return of thefluid at low pressure to the reservoir 17. The fluid used is anon-compressible liquid for an aircraft but any other liquid or air canbe used for applications other than aeronautical (land or naval).

Each fluid system comprises at least one accumulator with energy reserve19, the number being a function of the demands of the equipment forfluid under nominal pressure. The device of the invention describedbelow in the context of checking the state of an accumulator connectedto a fluid system can be adapted by a person skilled in the art to checkall the accumulators in the fluid system.

The accumulator with energy reserve 19 is here a hydraulic accumulatorwith metal bellows. In a variant, it is a membrane accumulator, that isto say one comprising an elastic wall delimiting the internal volume ofthis accumulator in two cavities.

On this distribution circuit 18 there is placed at least one pump 20 forpressurising the system. This pressurisation pump 20 is either aconstant-pressure pump or a constant-power pump. For applications in theaeronautical field, it is a piston pump in both cases.

The accumulator with energy reserve 19 is mounted on the high-pressureline HP of the fluid system 18 between the pressurisation pump 20 of thesystem and the consumers 4.

The device comprises a pressure detector 21 for measuring the pressureof the fluid in the high-pressure HP of this fluid system. This pressuredetector 21 is mounted on the distribution circuit 18 on the samehigh-pressure line HP where the accumulator with energy reserve 19 to betested is placed. It emits a measurement signal representing thepressure measured by the detector to a real-time processing unit 22having a non-volatile memory 23.

This pressure detector 21 advantageously makes it possible to measurepressures ranging up to 420 bar with a precision on the measurement ofless than ±4 bar. The pressure detector 21 must have a very rapidmeasurement acquisition speed in order to be able to respond todischarge times of much less than one second.

The real-time processing unit 22 is for example an onboard computer. Itcomprises electronic means 24 for measuring the interval of time ΔTseparating two predetermined pressure measurements P₁ and P₂ by thepressure detector 21. It also comprises means 25 for comparing thisvalue ΔT with a reference value stored in the non-volatile memory 23.These means are known to persons skilled in the art and will not bedescribed here. They may comprise by way of illustration an acquisitioncard mounted on the onboard computer 22 and software for comparing theinterval of time measured with the reference value stored in thenon-volatile memory 23.

The state of an accumulator 19 can be checked in non real-time wheneverthe pump nominally pressurises the fluid system in a stabilised fashionand then stops. This check can thus take place for example after amanoeuvre of the cargo door by maintaining the generation of pressurefor the length of time necessary for the test or after a manoeuvre of aconsumer 4 using a secondary power generation from a local fluid system.The processing unit in a pre-programmed manner initiates the procedureof comparing the interval of time ΔT separating two predeterminedpressure measurements P₁ and P₂ with the reference time T_(REF).

Advantageously, the pressure P₂ is the pre-charging pressure of theaccumulator and the pressure P₁ is such that 1/10 P_(F)<P₁<P_(F). Thisvalue of the pressure P₁ is however given by way of indication since,for more precision in the measurement, it would preferably be ensuredthat this interval of time ΔT separating two predetermined pressuremeasurements P₁ and P₂ is as large as possible, that is to say thepredetermined pressure P₁ is as close as possible to P_(F). The gaspre-charging pressure HE of this accumulator with metal bellows is, byway of example, 180 bar.

The real-time processing unit 22 can send a state signal from theaccumulator with energy reserve 19 to display means indicating to theoperator whether a maintenance operation is to be performed on thisaccumulator 19.

The invention also concerns an aircraft comprising at least anaccumulator with energy reserve connected to a fluid system, thisaircraft comprising a device for checking the state of an accumulatorwith energy reserve as described previously.

Finally, the invention concerns a method of checking the state of anaccumulator with energy reserve 19, this accumulator being connected toa fluid system.

This fluid system is first of all pressurised. For this purpose, atleast one pressurisation pump 20 as described above is used. This fluidis maintained at an operating pressure P_(F), for example 350 bar, forat least a time τ so as to ensure the stabilisation of the fluid system.The stabilisation of the system is achieved when no more variation inpressure and temperature is observed in the fluid system.

The pressurisation of the fluid system is then stopped and the way inwhich the system falls in pressure is determined. The gas pressure inthe second cavity of the accumulator with energy reserve 19 is thenderived from an analysis of the pressure discharge time ΔT of the fluidsystem.

For this purpose, the time ΔT taken by the system for passing from apredetermined pressure P₁ to a predetermined pressure P₂, withP₂<P₁<P_(F), is determined. Advantageously, the pressure P₂ is thepre-charging pressure of the accumulator and the pressure P₁ is suchthat 1/10 P_(F)<P₁<P_(F). If the accumulator is pressurised at thecorrect pressure, the discharge time of the system ΔT is greater than orequal to a predetermined reference time T_(REF). On the other hand, ifthe accumulator with energy reserve 19 is discharged and maintenancework is necessary, for example a re-pressurisation of the accumulator orreplacement with a new accumulator, then this discharge time ΔT isappreciably less than the predetermined reference time T_(REF).Advantageously, a processing unit 22 sends a state signal from thisaccumulator 19 to display means placed on an individual control panelfor this fluid system.

This reference time T_(ref) is for example previously determined bymeans of a reference accumulator, that is to say a correctly pressurisedaccumulator. The value of this reference time T_(ref) is preferentiallystored in a non-volatile memory 23 of a real-time processing unit 22receiving the measurement signals representing the pressure measured byat least one pressure detector 21 mounted on the high-pressure line HPof the fluid system.

FIG. 4 shows a method of implementing the method of the invention withthe device in FIG. 3. The X-axis 26 represents the time axis. Curve C₁shows the signal energising the pressurisation pump 20 of the fluidsystem, the maintenance of this pump 20 and its stoppage after anoperating time of 33 seconds. Curve C₂ represents the pressuremeasurements of the fluid system obtained by the pressure detector 21.The time for stabilising the fluid system is 30 seconds.

The time ΔT taken by the fluid system for passing from a predeterminedpressure P₁ of 330 bar to a predetermined pressure of P₂ of 140 bar is 3seconds. This discharge time of the fluid system is appreciably greaterthan the reference time T_(ref)=1 second determined with a referenceaccumulator with energy reserve. A comparison of these times indicatesthat the accumulator 19 is correctly pre-charged and requires nomaintenance work.

1. A method of checking the state of an accumulator with energy reserve(13, 19) that is connected to a fluid system, characterized in that thefollowing successive steps are performed; a) the fluid system ispressurized, b) this fluid is maintained at an operating pressure P_(F)for at least a time τ so as to ensure the stabilization of the fluidsystem, c) the pressurisation of the fluid system is stopped, d) thetime Δt taken by this system to change from a predetermined pressure P₁to a predetermined pressure P₂, with P₂<P₁<P_(F), is determined, e) thistime Δt is compared with a predetermined reference time T_(ref).
 2. Amethod according to claim 1, characterized in that step e) is performedby a real-time processing unit (22), the reference time T_(ref) beingstored in a non-volatile memory (23) of the said processing unit (22).3. A method according to claim 2, characterized in that, aftercomparison, the said processing unit (22) sends a state signal form thesaid accumulator (13, 19).
 4. A method according to claim 1,characterized in that the reference time T_(ref) is determined by stepsa) to d) using a reference accumulator.
 5. A method according to claim1, characterized in that P₂ is the pre-charging pressure of theaccumulator (13, 19).
 6. A method according to claim 1, characterized inthat the pressure P₁ is such that 1/10 P_(F)<P₁<P_(F).
 7. A methodaccording to claim 1, characterized in that the fluid is air.
 8. Amethod according to claim 1, characterized in that the fluid is aliquid.
 9. A device for implementing the method of checking the state ofan accumulator with energy reserve according to claim 1, the saidaccumulator (13, 19) being connected to a high-pressure line (HP) of afluid system, the said fluid system comprising at least one pump (20)for pressuring the said system, characterized in that it comprises; areal-time processing unit (22) having a non-volatile memory (23), atleast one pressure detector (21) for measuring the pressure of the fluidin the high-pressure line (HP), the said detector (21) sending to theprocessing unit (22) a measurement signal representing the pressuremeasured by the said detector (21), and in that the said processing unit(22) comprises electronic means (24) for measuring the interval of timeΔt separating two predetermined pressure measurements P₁ and P₂, andmeans (25) for comparing this value Δt with a reference value stored inthe said non-volatile memory (23).
 10. A device according to claim 9,characterized in that the said pressure detector (21) can measurepressures ranging up to 420 bar.
 11. A device according to claim 9,characterized in that the said real-time unit (22) sends a state signalfrom the said accumulator (13, 19) to display means.
 12. An aircraftcomprising at least one accumulator with energy reserve (13,19),characterized in that it comprises at least one device according toclaim 9.